Electrical switching device



April 29 1924. 4 1,491,867

' G. W. KUHN ELECTRICAL SWITCHING DEVICE Filed July 24. 1920 2Sheets-Sheet l //4 van 70/: 6, W. K 01/4.

Patented Apr. 29, 1924.

UNHTED STATES PATENT orrre GEORGE W. KUHN, OF NEW YORK, N. Y., ASSIGNORTO AMERICAN TELEPHONE AND TELEGRAPH COMPANY,'A CORPORATION OF NEW YORK.

ELECTRICAL SWITCHING DEVICE.

Application filed July 24, 1920. Serial No. 398,698.

T 0 all whom t'r' may concern.

Be it known that I, GEORGE W. KUHN, residing at-New York, in the countyof New York and State of New York, have invented certain Improvements inElectrical Switching Devices, of which the following is a specification.

This invention relates to electrical switching devices, and moreparticularly to a switching device adapted for insertion in a telephonecircuit and designed to effect successively a plurality of differentelectrical connections without rendering discon-v tinuous the connectionbetween the tip and ring sides of the said circuit.

Devices of, this nature heretofore used belonging to that class designedto connect atelephone circuit, such as trunk circuit with an operatorstelephone circuit, or to bridge across the said trunk circuit a holdingcoil whose function was to maintain in its operated condition certainapparatus associated with the trunk circuit, consisted usually of a keyhaving two groupsof con tacts, which, for the purpose of description,may be referred to asthe right-hand and left-hand groups, although inpractice these groups may occupy other relative positions. The trunkcircuit terminated upon certain springs of one of these groups and waslooped back or strapped through to the springs of the other group ofcontacts when the springs of both groups were in their normalnon-operated position. The telephone set circuit-was connected withcertain springs of the said first group and the hold ing coil circuitwas connected with certain springs of the other of the said groups ofsprings.

Associated with each group of springs were certain master springsadapted to be engaged by the cam of the key and when so engaged,designed to operate the other contacts of the same group with which theoperated master springs were associated. Thus, if the cam of the keywere moved so as to operate the master springs associated with theright-hand group, contacts necessary to connect the operators telephoneset with the line would be made. If the cam were moved so as to operatethe master springs of the left-hand group, the incoming circuit would beconnected with the circult of the holdin coil. If the cam were left inits norma position, which operatively would be midway between thetalking and the holding positions of the said key, the master springs of'neithergroup would be operated, in consequence of which neither thetelephone set northe holding coil would be connected to the incomingline sir-- cuit, and, furtherinore, the circuit between the tip and ringsides of the incoming line would be maintained opened. If the incomingline has associated with it a supervisory relay, the operation of whichis dependent upon the maintenance of aclosed circuit between the tip andring sides of the line, such relay would be released when the cam was inits normalneutral position re-- sulting in the release of switches,where the key is used in a system employing automatic switches, and inthe actuation of a supervisory signal where the key is used in a manualtelephone system.

Thus, if the operator at the incoming position, after answering thecall,finds it necessary to disconnect her telephone set from the. incomingtrunk circuit, but desires to hold the latter, she will move the cam ofthe key from its right to its left-hand position, which necessitatespassing through the normal neutral position of the key, during whichtime the circuit between the tip and ring sides will be opened. If thekey is operated relatively slowly, the supervisory relay may bereleased, thusreleasing switches in an automatic telephone system, orcausing theactuation of a supervisory signal in a manual system, thusgiving to the operator a disconnect signal. This inadvertent opening ofthe line circuit thus results in a disconnection of the parties in anautomatic system, or the giving of a disconnect signal to the operatorin a manual system, and leads to confusion of operation.

It is the object of the present invention to provide a switching deviceby means of which the tip and ring sides of the incoming circuit willnot be opened when the operator moves the cam of the key from thetalking to the holding position, or vice versa. Thisinvention will bebetter understood from the following description when read in connectionwith the attached drawings, represented-by Figs. 1 and 2, which show anapplication of the invention to a manual telephone system, and Fig. 3which shows an application of the invention to an automatic telephonesystem.

In Fig. 1 of the drawings L represents a trunk line which, for thepurpose oi description, will be assumed to be of that type extendingfrom a switchboard A to a repair clerks desk 13. The line L terminatesat the switchboard A in a jack 29 with which is associated the lamp 31by means of which the repair clerk may signal the operator at A. Xrepresents a portion of a cord circuit which may be of the usualsubscribers type located at the switchboard A having associatedtherewith a plug 30 which is adapted to be inserted in a jack 29. Thecord circuit X of which approximately one end is shown, comprises, inpart, a repeating coil 1 to which battery is connected in order tofurnish energy to the line with which the cord circuit may be connected.Connected with the ring side of the cord circuit is a supervisory relay40, havingassociated therewith a lamp 41, which servesas the supervisorysignal of the cord circuit. At the repair clerks desk B there may belocated a telephone circuit X which is adapted to be connected with thesprings of the key K Associated with the trunkcin cuit L and located atthe repair clerks end of the said circuit, are the relays-32 and 33, andthe key K The key K is so designed that the cam thereof is adapted tooccupy normally the position represented by the circle It will be seenthat when the cam is in this position the master springs and the othersprings controlled thereby, included within the right-hand group ofsprings, are spread apart and all of the contacts of said springs areopened. If the cam be moved to its middle position b, the master springsof the right-hand group and the associated springs will be released, andin returning to their natural position, they will close the contacts ofthe various adjacent springs of this group. This, as will be seen moreclearly, later serves to connect the trunk line L with the telephonecircuit X If it is desired to disconnect the telephone set circuit "fromthe trunk line but to maintain operated the supervisory relay of thecord circuit X the cam may be moved into the position designated c. dWhen thecam is thus operated, the master springs of the-lefthand groupand the springs associated therewith will be moved so as to disconnectthe telephone set from and to bridrie the holding circuit across thetrunk circuit.

Having in mind the foregoing description of the parts shown in thedrawings, thisinvention will be more fullyunderstood from the followingdescription of its modeof operation.

Let it be assumed that the operator at A desires 'to obtain from therepair clerk at the position B certain information. i The operator at Awill insert the plug 30 of the cord circuit X jack 29 and will thenapply ringing current by means of the key K to the line L which, flowingthrough the condenser 50- and the right-hand winding of relay 32 willcause the operation of said relay. Relay 32 is locked up over a pathextending from ground, the left-hand winding of relay 32, contacts 16 ofrelay 33 and contacts 4 of relay 32 to grounded battery. By the closingof the contacts 4 of relay 32, current will flow through the outerarmature of relay 32 and contacts 4 through contacts 6 of relay 33 andthrough lamp 43 to ground, causing the lighting of this lamp. The clerkat the desk B, noting the lighting of the lamp 43, will operate the keyK by moving the cam into the position b. Helay 34 will then be energizedover a path e2;- tending from ground, througl'rthe upper lefthandwinding of repeating coil 1, through theupper normal contacts of key Ktips of plug 30 and jack 29, contacts '7 and contacts 8 of key K windingof relay 34, contacts 9 and contacts 10 of key K right-hand winding ofrelay 32, rings of jack29 and plug 30, lower normal contacts of key Kwinding of relay 40, and lower left-hand winding of repeating coil 1 togroundedbattery. Relay 34, in operating,

completes a circuit at its armature and front contact for relay 3 5.Relay 35, in operating, connects the operators telephone circuit X withthe talking conductors 11. The tip and ring sides of the line L are alsoconnected through contacts 12, 14, and 13 and 15 respectively with thetalking conductors 11, and, therefore, with the telephone circuit X theoperation of key K contact 18 is also closed, thereby causing theoperation of relay 33 over a path traceable -from grounded battery,lefthand winding of relay 33, contacts 18 and 60 of key K to ground.Relay 33, in operating, locks up over a path extending from ground,right-hand winding, front contact, and. righthand armature of relay 3 3,sleeves of jack 29 and plug 30 and thence through lamp 41, resistance45, armature and front contact of relay in parallel to grounded battery.Since the supervisory relay 49 has already been operated by a low ofcurrent there-through when key K was moved to position Z), a shunt pathwas established around the lamp 4-1, said shunt path'including the frontcontact and armature of relay 40 and resistance 45, so that lamp 41will. no longer glow. Relay 33, in operating, opens the circuit for lamp43 at contact 6, thereby extinguishing lamp 43. The lOCl.'- ing circuitfor relay 32 is also opened atcontact 16 but relay 32 remains energizeddue to current flowing through its right hand winding from the batteryat repeating coil 1,.through the winding of relay 34.

If the clerk at the desk B desires to disconn h -te phen m h n min linecircuit L but does not desire to give tothe opertor at A a disconnectsignal, the

springs, the contacts 14 and 15 are opened, V

whereby the conductors 11 are disconnected from the telephone set Xthereby permitting the telephone set to be used with other trunkcircuits. Contacts 8 and 9 of this group are also opened, but contact 21is closed. It will be seen, therefore, that the movement of the camtoposition serves to release relay 34, which in turn releases relay 35.The tip and ring sides of the line L however, remain connected togetherthrough contacts 7, 21 and of the key K and the right-hand winding ofrelay 32. The supervisory relay 40, therefore, remains energized, andthe lamp 41, associated therewith, remains extinguished so that theoperator at A does not receive a disconnect signal as a result of themovement of the cam key K from it's talking to its holding position. 7

When the clerk at B desires to communicats with the operator at A, hewill move the cam back again to the position b,thereby connecting thetelephone set circuit X with the line L Upon the completion of theconversation and when the connection is no longer desired, the cam ofkey K will be moved into position a. This serves .to open all of thecontacts of said key and thereby breaks the connection between the tipand ring side of the line if, which results in the releasing )of therelay. 40. The lamp 41, therefore, will be lighted due to the removal ofthe shunt around it, and the operator at A will accordingly remove theplug 40 from the jack 29 and restore the circuitto normal condition.

Fig. 2 shows a cord circuit X equlpped to give a flashing recall signaland is adapted for use in connection with I the trunk circuit L The cordcircuit X a portion only of which is shown, has a plug which is adaptedfor insertion in the jack 29. This cord circuitcomprises a repeatingcoil to which a battery for'talking and signaling purposes is connected.Connected to the ring side of the answering cord is the followingmanner.

X isa key K which is adapted tobridge the operators telephone set (notshown) across the circuit or to apply ringing current to the line,depending upon the direction. in'which the key is operated. I

Having in mind the foregoing description of the parts of the circuit andthe function performed by each part, this invention will be betterunderstood by the following description of its mode of operation. I

I Let it'be assumed that the operatoror clerk-at B desires to obtainacertain sub- 'scriber, the; clerk will signal. the operator at A bymoving the key K to position 1),

which serves to lightthe lamp 31. The operator atA will insert plug 60into jack 29 and operate the listening key K which serves to connect hertelephone set with her cord circuit 'X plug 60 into jack 29, the lamp 82would tend to light by a flow of current from grounded battery throughlamp 82, resistance 98, sleeves of plug 60 and jack '29, right-handarmature and back contact of relay 33, and resistance 99 to ground. Thelamp is, however, prevented from lighting by the operation of relays and84, which establish a short-circuit around the lamp in It will berecalled from the description of Fig. 1 that when the key K was moved.to position b, the connection was established between the tip and ringsides of the line D, and consequently across the conductors of the cordcircuit X This results in a flow of current from the battery [connectedto the winding of repeating coil 70, through the winding of supervisoryrelay 80, causing the operation of supervisory relay 80, whereuponcontacts 94 of'supervisory relay 80 are closed. VVhen' the operatorinserted the plug 60into the jack 29 in order to take up the call, sheoperated the key K in a left-hand direction in order to connect hertelephone set with the circuit which connected conductor 97 throughcontact 92 to ground. This established a circuit from grounded battery,ri t-hand winding of relay 84, conductor 9%, and contacts 92' of key Kto ground, thereby causing the op eration of relay 84. Relay 84, inoperating,

locks up over a path extending from grounded battery, right-handarmature and front contact of relay 84, contacts 94 of the relay 80,front contact and left-hand armature of relay 84,lei"t-hand winding ofrelay 84, through resistance 98, sleeves ofplug 60 and jack 29,right-handarmatur'e and front contact of relay '33, and right handwinding of relay 33 to ground. This establishes a shunt path around thelamp 82 so that it remains extinguished.

Let us assume that after the desired connection hasbeen established andcommuni-- Upon insertion of the-- cation thereover has been completed,that the clerk at B restores the key K to the position a momentarily andthen moves to position b in order to again signal the operator at A.When the key K was moved to position a, the connection between the tipand ring sides of the circuit was opened and the supervisory relay 80 isdeenergized which permits the opening of the contact 94. This results inthe deenergization of relay 84 and causes the lighting of the lamp 82.This will indicate to the operator that the parties have disconnected,and unless some different 7 signal is given to her as when the key K ismoved to the position b, the operator would take down the cords of thecircuit. This is prevented, however, when the key is moved into positionb by the inauguration of What is known as the flashing recall signal.Thus, when the key K is in position b, relay 80 will be operated which,when relays 33, '84: and 85 are not energized, establishes a circuitfrom grounded battery, armature and back contact of relay 85, left-handwinding of relay 83, normal right-hand contacts of relay 84, contact 94,normal left-hand contacts of relay 8%, resistances 87 and 98, sleeves ofplug and jack 29, right-hand armature and back contact of relay 33, andresistance 99 to ground. This establishes a shunt path around lamp 82,which extinguishes the lamp. The flow of current through the left-handwinding of relay 83 energizes this relay, and if the contacts of theinterrupter 90 are in a position to stablish a connection to ground,current will flow from grounded battery, winding of relay 85, right-handWinding of relay 83, front contact and armature of relay 83, throughinterrupter 90 to ground. Relay 85 will be energized thereby, and at itsarmature and front contact, a circuit will be closed for buzzer 91, and,at the same time, the shunt path will be removed from the lamp 82, thuspermitting said lamp to light. It will be seen, therefore, that by meansof this arrangement the interrupter 90 causes the intermittentenergization of relay 85 and the intermittent lighting of lamp 82whereby a flashing signal is given to the operator which indicates thatthe party whose line is connected with that cord desires to recall theoperator.

In the arrangement of key switches heretofore used in which the campassed through a neutral position between the talking position and theholding position whereby the connection between the tip and ring sidesof the line was momentarily opened, there was switching device of thetype embodying the principle o'l this invention, it is possible totransfer the trunk circuit from the telephone set to a holding circuitand vice versa without opening the circuit of a supervisory cord relayand thereby causing an involuntary operation of the said supervisoryrelay which would produce a false disconnect signal.

.In Fig. 3 of the drawings which represents an embodiment of theinvention as applied to an automatic telephone exchange system, there isshown a trunk line L extending from a repair clerks desk or operatorsposition B to an automatic telephone exchange. The trunk line Lterminates at the operators position in the key K and has associatedtherewith a lamp 133 by means of which the operator may be signaled onincoming calls from the automatic telephone exchange. An impulse senderS g is provided for the operator at position B for the purpose ofcontrolling switches at the automatic exchange 011 outgoing calls tostations of said exchange. The trunk line L terminates at the automaticexchange in a nonnumerical switch N and is multiplied to contacts of aconnector switch, such as C. The non-numericalswitch N and the connectorswitch C are schematically represented only, since they form no part ofthe present invention, the inventive idea of the disclosure beingcapable of adaptation to any wellknown .automatic telephone exchange.Switches of the type herein indicated are fully disclosed and describedin the patent of F. A. Stearn et al., No. 1,395,977, granted November 1,1921.

Having in mind the foregoing description of the parts shown in Fig. 3 ofthe drawings, the invention will be more fully understood from thefollowing description of a call from the operators position to a stationof the automatic exchange, and a call from a station of the automatictelephone exchange to the operator. 7 Assuming that the operator orclerk at position B desires a connection with a station such as H, atthe automatic telephone exchange, the operator at B by moving the key Kto position causes the ene'rgization of relays 136 and 134 of the trunkcircuit over a path extending from grounded bat- .tery, left-hand indingof relay 134;, winding of relay 136, contacts 118 and 160 of key K andcontacts 152 of sender S to ground. Relay 136 in operating shortcircuits condenser 137, and places a bridge across the trunk conductorsL said bridge including the right hand winding oi relay 135 and contacts of relay 136 thereby causing the operation of line relay .101 ofthe non-numerical switch N over a path extending from ground, uppernormal contacts of relay 102, righthand winding of relay 135, contactsof relay 136, lower normal contacts of relay 1.02 and right-hand windingof relay 101 to grounded battery. Relay 131 of the operators telephoneset circuit is also energized over a path extending from ground, throughthe upper normal contacts of cut-oil relay 102, contacts 112 and 114 013key K upper talking conductor 111, coil 130, winding of relay 131, backcontact and armature of relay 132, contacts 151 of impulse sender S,lower talking conductor 111, contacts 115 and 113 of key K lower normalcontacts of cut-off relay 102, and right-hand winding of relay 101 togrounded battery. Relay 101, of the non-numerical switch N, in Ienergizing, closes a circuit for a stepping magnet (not shown) under thecontrol of which the brushes 108, 109 and 110 of switch N are advanced.As soon as the brush 110 passes off of normal contact 125 and intoengagement with segment 123, battery potential is connected to themultiple test terminal, such as 182, appearing in the banks of finalselectors having access to the line, over conductor 122, brush 110 andsegment 123 to grounded battery, and relay 138 of the trunk circuit L isenergized over a path extending from grounded battery, segment 123,brush 110, and the winding of relay 138 to ground. Under control of thestepping magnet (not shown) of the non-numerical switch N, the brushes108, 109 and 110 are advanced until the terminals 192 and 19 1 of anidle switch, such as C, are reached, whereupon cut-off relay 102 isenergized and the line L is extended through to the switch 0. It will beunderstood that there may be a number of selector switches interposedbetween the nonnumerical switch N and the connector switch l/Vhen relay131 of the operators telephone set was energized, it completed a circuitthrough its contacts for relay 190, said circuit including contacts 152of'sender S. Relay 190 in energizing telephonically connects theoperators telephone set to the conductors 111.

The operator at position B may now actuate the impulse sender S tocontrol the setting of the connector switch C upon the terminals of adesired station, such as H, in the well-known manner. Upon the initialmove ment of the impulse sender, contacts 150 are closed and remainclosed during the'movement of the sender. The closure of the contacts150 completes a circuit for the energization of relay 132. Relay 132, inenergizing, bridges coil 130 directly across the tip and ring conductorsof the trunk circuit L and opens the circuit for relay 131, which indialing.

retracting its armature opens the circuit for relay-190; Rela'y 190opens the operators from across the trunk conductors L during,

dialing. As the impulse sender returns to normal, the bridge across theconductors 111, including coil 130, front contact and arma-- ture ofrelay 132 and contacts 151 of im- -pulse sender S, is intermittentlyopened thereby conveying impulses to the connector switch. C at theautomatic telephone exchange in the well-known manner. At the end ofeach series'of impulses, the contacts 150 of impulse sender S areopened, thereby permitting the deenergization of relay 132. The contacts152 of impulse sender S are closed at the end of each series of impulsesthereby connecting the bridge, consisting of the right-hand winding ofrelay 135, the armature and front contact of relay 136, across thetrunkconductors L After sending a suflicient number of impulses to set thebrushes 161, 162 and- 163 or the connector switch C upon the terminals164, 165 and 166 respectively, and if the line at such station has beenfound idle, ofi'-normal contacts 167 will be closed thereby placing thebusy test upon the terminal 166 of the desired sta-' tion. Station H maythen be signaled in the well-known manner and after the re sponse ofsuch station, the operator at position 13 and the converse.

party at'station H may If the operator at the desk B desires todisconnect the telephone set from the trunk circuit L and does notdesire to'release the connection, the said operator will now move thecam ofthe key K into position 0 By the operation of the master springsin the left-hand group of springs, the contacts 114,

and 160 are opened and contacts 121 are closed. The opening of contacts114 and 115 disconnects the tip and ring conductors from the telephoneset :X thereby permitting the telephone set to be used with other trunkcircuits. The closure of contacts 121 holds relay 136 energized whencontacts 160 are opened,'thereby maintaining the bridge across the tipand ring conductors of the 'Upon completion of the conversation and whenthe connection is no longer desired,

the cam of key K will be moved into'position a This serves to open allthe contacts of the right-hand group of the key. K

whereupon relay 136 is released and the of the trunk circuit and cut-offrelay. 102

of the non-numerical switch associated with the trunk circuit L will beenergized over a path extending from groundedbattery, contacts 167,brush 163, terminal 182 conductor 122 and thence in parallel, one pathextending through the winding of relay 138 to ground and the other pathextending through brush 110, normal contacts 125, lower and upperwindings of ClltrOfi relay 102 to ground. Ringing current may beprojected over the terminal 180, conductor 148, through the right-handwinding of relay 135 and condenser 137, which are normally bridged inseries across the trunk conductors L and conductor 147 to terminal 181.Relay 135 is thereupon energized and locks up over a path extending fromgrounded battery, right-hand armature and back contact of relay 134, theinner armature, front contact and winding of relay 135 to ground. At thefront contact and outer armature of relay 135, a circuit extendingthrough the left-hand armature and back contact of relay 134 iscompleted for lamp signal 133.

The operator at position B noting the signal 133, will actuate the key Kby moving the cam into position 6 whereupon a circuit for relays 136 and134 of the trunk circuit L will be completed over a path extending fromground, contacts-152 of sender S, contacts 160 and 118 of key K andwindings of relays 136 and 134 to grounded battery. Relay 136 isenergized, and in attracting its armature short circuits condenser 137and bridges the right-hand winding of relay 135 directly across the tipand ring talking conductors thereby causing the tripping of the machineringing in the well known manner and the advancement of the connectorinto the talking position. Relay 134 is also energized and in attractingits lefthand armature, interrupts the circuit for lamp signal 133thereby extinguishing said signal and at its right-hand armature andfront contact completes a locking circuit for itself over a pathextending from ground, armature and front contact of reoperated lay 138,the right-hand winding, front con- .tact and armature of relay 134 togrounded battery. Belay 134 in energizing also interrupts the lockingcircuit forrelay 135, but

this relay does not retract its armatures since.

it is maintained energized over a path extending from ground, upperright-hand winding of repeating coil 170, brush'161, terminal 180,conductor 148, right-hand winding of relay 135, armature and frontcontact of relay 136, conductor. 147, termi nal 181, brush 162, windingof relay 175 and lower right-hand winding of repeating coil 170 togrounded battery.- When the operator at position B operated the key K bymoving-the cam into the position b coil 130 and winding of relay 131 inseries with the back contact and armature of relay 132 and contacts 151of impulse sender S of the operators telephone set circuit were alsobridged across the talking conductors of the trunk circuit. Relay 131associated with the operators telephone set X is then energized over apath extending from grounded battery, upper right-hand winding ofrepeating coil 17 0 associated with the connector switch, brush 161,terminal 180, conductor 148, contacts 112 and 114 of key K coil 130,winding of relay 131, back contact and armature of relay132, contacts151 of'impulse sender S, contacts 115 and 113 of key Kflconductor 147,terminal 181, brush 162,

winding of relay 175 and the lower right- 7 111 and-the operator'atposition B may now converse with the calling station.

If, after conversation with the calling station, the operator at desk 13desires to disconnect the telephone set X from the trunk circuit L butdoes not desire to re leasethe switches at the automatic exchange, thesaid operator will move the cam of the key K* into position 0 By theoperation of the master springs in the lefthand group of springs, thecontacts 114 and 115 are opened whereupon-the tip and ring conductors ofthe trunk circuit L are disconnected from the telephone set X therebypermitting the telephone set to be used with other trunk circuits. theleft-hand group are also opened, but contacts-121 are closed beforecontacts 160 are opened thereby maintaining relay 136 and consequentlymaintaining the bridge across the talking conductors of trunk circuit LThe telephone set is thus disconnected and free for use but the switchesat the automatic exchange are held by the bridge of relay 135 andcontacts of relay 186. The switches are thus not released as a result ofthe movement of the cam K from the talking to the holding switches.

When the operator at the position B deires to converse with the callingstation, the said operator will move the cam back into the position 19thereby connecting the telephone set circuit X with the line trunkcircuit. 7 v

Upon completion of conversation and when the connection is no longerdesired, the cam of key K will be moved into position 0, This serves toopen all contacts of the right-hand group ofkey K thereby removing thebridge from across the tip and ring conductors of the trunk circuit Land causing the release-of the switches at the automatic exchange in thewell-known man- 'JIQI. The circuit is then ready for the next call. 7

What is claimed is:

1. In a signaling system, acircuit having associated therewith asupervisory relay, a

holding circuit connected to said first circuit, a third circuit, and asingle switch for transferring the connection of the said first circuitfrom the said holding circuit to the said third circuit and vice versa.,Without opening the circuit embracing the said relay.

2. In a signaling system, a circuit having associated therewith a relay,a supervisory signal controlled thereby, a holding circuit connected tosaid first circuit, a third circuit, and a single switch fortransferring the connection of the said first circuit from the saidholding circuit to the said third circuit and vice versa, withoutopening thecircuit embracing the said relay and preventing theindication of a disconnect signal.

3. In a telephone system, a circuit having a supervisory relay, aholding circuit associated with said first circuit, a telephone circuit,and a single switch associated with said first mentioned circuitdesigned in its normal position to maintain open the circuit of saidsupervisory relay but arranged to close the circuit of said supervisoryrelay when the said circuit is connected to said telephone circuit, andto maintain the said supervisory relay circuit closed when the saidcircuit is transferred from said telephone to said holding circuit.

4. In a telephone system, a circuit having a supervisory relay, aholding circuit, a telephone circuit, and a single switch associatedwith said first mentioned circuit designed in its normal position tomaintain open the circuit of said supervisory relay but arranged toclose the circuit ofsaid supervisory relay when the said circuit isconnected to said telephone circuit, and to maintain the saidsupervisory relay circuit closed when the said circuit is transferredfrom said telephone to said holding circuit and vice versa.

5. In a signaling system, the combination of a line circuit havingassociated therewith a supervisory signal adapted to indicate circuitconditions, a telephone circuit, a holding circuit, and a single switchdesigned normally to maintain open the circuit of said supervisorysignal but adapted to close the supervisory signal circuitwhenever thesaid line circuit is connected to the said telephone circuit, and tomaintain the said supervisory signal circuit closed when the said linecircuit is transferred from" said and having a supervisory. relayassociated therewith, a second circuit, a third circuit, and a slngleswitch for connecting sald first circuit with elther said second or saidthird circuit without opening the connection be-.

tween the sides of the said first circuit, whereby the said supervisoryrelay may be maintained in its operative position.

7. In a signaling system, the combination with a circuit havingconnected therewith, a cord circuit containing a supervisory relay, of aholding circuit connected to-said first circuit, a third circuit, and asingle switch for transferring the connection of the said line circuitfrom the said holding circuit to said third circuit without opening lay,of a telephone circuit, a second circuit.

including a relay controlling said telephone circuit, a holding circuitand a multi-position switch adapted in one position to connect saidsupervisory relay in circuit with said second mentioned relay wherebysaid relays operate and said telephone circuit is connected to the cordcircuit, and in another position to interchange said second circuit andsaid holding circuit to maintain said supervisory relay operated and todisconnect said telephone circuit from said cord circuit.

9. In a signaling system, the combination with a trunk circuit, a cordcircuit equipped with a supervisory relay, aholding circuit for saidrelay, and a switching device having a normal and two successiveoperative positions, said device being adapted in its normal position todisconnect said trunk circuitfrom said cord circuit, in one of itsoperative positions to connect said trunk circuit with said cordcircuit, and in its other operative position to connect said cordcircuit with said holding circuit.

10. In a signaling system, a first circuit having a supervisory devicetherein, a second circuit to be associated with said first circuit, aholding circuit to prevent the deenergization of said supervisorydevice, and a switching device comprising a key having a normal and aplurality o1 successive operative positions whereby said first circuitand said second circuit will be normally disconnected, said firstcircuit and said second circuit will be connected when said switchingdevice is moved to one of its operative positions, and said firstcircuit and said holding circuit will be connected when said switchingdevice is moved to another of its operative "positions.

nect said set to said circuit, to disconnect said'set from said circuit,and to substitute said second circuit.

13. An operators telephone set, a circuit, a second circuit, a switchhaving contacts in said first circuit, and connections for saidswitchwhereby said operatorstelephone set and said second circuit may beinterchangeably connected to said first circuit without 7 saidsupervisory circuit disassociated when a said trunk is seized at one ofsaid positions, in another position to associate said telephone circuitwith said supervisory circuit, and in another position to disassociatesaid telephone circuit and said supervisory circuit and to substitute aholding circuit for said telephone circuit, thereby maintaining saidsupervisory circuit closed. v

15. In a signaling system, the combination with a trunk circuit, a cordcircuit equipped With'a supervisory relay, a telephone circuit, a relayfor connecting said telephone circuit with said trunk circuit, and aswitching device having a normal and'two successiveoperative positions,said device being adapted in its normal position to maintain saidtelephone circuit disassociated from said trunk circuit, in one of itsoperative positions to establish a circuit for said relay whereby saidtelephone circuit is connected to said trunk circuit and saidsupervisory relay operated in series with said relay, and in its otheroperative position to disconnect said relay and said telephone'circuitfrom said trunk circuit and to substitute a holding circuit'for saidsupervisory relay.

In testimony whereof, I have signed my name to this specificationthi's'22nd dayof July 1920.

GEORGE W. KUHN.

